US4374703A - Control system for papermaking machine headbox - Google Patents

Control system for papermaking machine headbox Download PDF

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Publication number
US4374703A
US4374703A US06/223,564 US22356481A US4374703A US 4374703 A US4374703 A US 4374703A US 22356481 A US22356481 A US 22356481A US 4374703 A US4374703 A US 4374703A
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Prior art keywords
headbox
control system
actuators
multivariable
pulp
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Expired - Fee Related
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US06/223,564
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English (en)
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Louis Lebeau
Guy Bornard
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Centre Technique de lIndustrie des Papiers Cartons et Celluloses
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Centre Technique de lIndustrie des Papiers Cartons et Celluloses
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
    • D21G9/00—Other accessories for paper-making machines
    • D21G9/0009—Paper-making control systems
    • D21G9/0027—Paper-making control systems controlling the forming section
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F1/00—Wet end of machines for making continuous webs of paper
    • D21F1/06—Regulating pulp flow
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S162/00—Paper making and fiber liberation
    • Y10S162/06—Moisture and basic weight
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S162/00—Paper making and fiber liberation
    • Y10S162/09—Uses for paper making sludge
    • Y10S162/10—Computer control of paper making variables
    • Y10S162/11—Wet end paper making variables

Definitions

  • headbox it is meant the device which assures the projecting of a paper pulp onto a wire or between wires at the front end of a paper machine, whether said device actually has the appearance of a box or whether it has any other shape, such as for instance that of a plurality of channels, namely a so-called "multi-channel" box.
  • the parameters such as the speed of the jet of pulp emerging from the headbox, the concentration of the pulp, and the rate of flow of material are determinative of the properties of the paper which is finally obtained. Thus, it has been attempted to effect automatic adjustments of these parameters.
  • Said first adjustment may comprise the control of a valve for the introduction of air into the box by a monovariable controller which receives as input information a level set point information and a level measurement information which is supplied by a level sensor, and the control of the pump supplying the box with dilute pulp by a monovariable controller which receives as input information a jet speed set point information and a jet speed measurement information given, after transformation of the signal, by a sensor of the total pressure present in the box.
  • the second control maintains a constant ratio between the speed of the wire and the speed of the jet of pulp.
  • a wire speed information and a jet speed information are detected, the ratio of these two data is formed and this ratio is sent, at the same time as a set point, to a controller which acts on one of the actuators, that relating to the admission of air or that relating to the fan pump, either directly or indirectly by determining the set point of another controller which is then the level controller or the jet speed controller referred to above.
  • the second control may, in the same manner, maintain constant not the ratio between the wire speed and the speed of the jet but the difference between these two variables.
  • a third control is assigned to the basis weight and moisture. It comprises two measurement sensors generally combined in the same head, located downstream of the drying section which follows the headbox, the wet section, and the press section of the paper machine, and two sensors receiving at the input basis weight set point and a moisture set point and the measurement signals supplied by these sensors sending two control signals on the one hand to a thick-stock valve located upstream of the fan pump or possibly to a set point of a local control of this pulp flow and on the other hand either to at least one steam valve or possibly the pressure control set point or to the device adjusting the speed of the machine.
  • dry stock control One frequently also finds a feed forward correction of variation of the consistency of the thick pulp which modifies the rate of flow of pulp as a function of this consistency. This correction is currently referred to as "dry stock control”.
  • Another difficulty relates to the fact that one is confronted by a process having very strong couplings between the different parameters.
  • the hydraulic control can cause a deterioration of the substance flow rate.
  • the present invention is based on an entirely different concept of control.
  • the invention thus proposes, in a system for the control of a paper machine headbox having sensors for the measurement of the parameters of the process and actuators of the process, functionally connecting at least most of the sensors to an at least equal number of actuators via a multivariable centralized control device which makes it possible to control each actuator by the taking into account and processing of the measurement information of one or more sensors, and causing the measurement information from each of the sensors functionally connected to the actuators to act on one or more actuators so as to obtain a resultant action in which only the parameter measured by this sensor is influenced while the secondary repercussions on the other parameters are eliminated.
  • the invention permits rapid intervention taking into account the information on the substance flow rate at the headbox, eliminating the usual disturbing influences due to the hydraulic variables of the process.
  • This information can be calculated on the basis of a measurement of the concentration in the headbox, which measurement can be supplied by a conventional continuous concentration sensor, the master role played by the basis weight sensor of later action making it possible to compensate for the errors inherent in such apparatus.
  • these monovariable local controls operate permanently, the centralized control device acting on the set point of these local controls.
  • FIG. 1 shows an entire headbox of a paper machine
  • FIG. 2 shows synoptically the control system in accordance with the invention
  • FIG. 3 shows an example of a multivariable control system in which the various signals have been separated
  • FIG. 4 shows an example of a multivariable centralized control device used in this control system
  • FIG. 5 shows another example of a multivariable centralized control device
  • FIG. 6 shows a multivariable control system with adjustment of the basis weight
  • FIG. 7 shows a multivariable control system with adjustment of the speed of the jet with respect to the speed of the wire
  • FIGS. 8 and 9 show fluctuations recorded in the case of a conventional control and in the case of the control in accordance with the invention, respectively,
  • FIG. 10 shows a multivariable control system in the case that the slice opening is not automatically controlled
  • FIG. 11 shows a multivariable control system in the event that the level in the box is maintained by a monovariable control loop
  • FIG. 12 shows a multivariable control system in the case of an headbox with overflow
  • FIGS. 13 and 14 show a multivariable control system combined with monovariable controls.
  • FIG. 1 there has been shown schematically an entire conventional headbox into which pulp arrives via a pipe 1 provided with stock valve 2 and is entrained, after dilution, by a fan pump 3 into a pipe 4 which connects with a cleaner 5 connected by a pipe 6 to a headbox 7, from where the diluted pulp emerges at 8 in a jet which projects it onto an endless wire 9 driven at high speed, below which a pit 10 recovers the drainage water, this wet section being followed by a press section and a dry section, which have not been shown in this figure.
  • An air cushion 11 is formed in the headbox 7 by air supplied by a blower pump 12 into a pipe 13 provided with an air valve 14.
  • a recycle pipe 15 provided with a recycle valve 16 is mounted in parallel with the fan pump 3.
  • actuators Four actuators are provided to effect adjustments: an actuator U 1 which controls the stock valve 2; an actuator U 2 which controls the speed of rotation of the fan pump and/or the recycle valve 16 (which will be referred to simply as pump actuator); an actuator U 3 which controls the speed of the blowerpump 12 and/or the air valve 14 (which will be called simply the air-valve actuator); and an actuator U 4 which controls the opening of a slice 17 located on the outlet 8.
  • the conventional controls consist in providing a plurality of monovariable control loops each of which comprises one of the actuators and a measurement sensor for example one loop comprises a sensor detecting the level of pulp in the headbox 7 and a controller acting on the air valve 14, another loop comprises a sensor detecting the total pressure in the headbox 7 and a controller acting on the speed of the motor of the fan pump 3, and yet another loop comprises a basis weight sensor arranged at the output of the drying section (not shown) and a controller acting on the stock valve 2.
  • a multivariable centralized control device 18 which receives at least most of the parameter measurement information given by the sensors which information has been diagrammatically indicated by the output vector Y, as well as all the corresponding set point information indicated diagrammatically by the set point vector Z and which sends multiple orders indicated diagrammatically by the vector U, to actuators of the process 19 which is formed by the headbox and its related parts.
  • These disturbances concern parameters which act on the outputs Y, but which can be measured.
  • the invention makes it possible to compensate for these disturbances in advance, before their effect is received on the outputs Y.
  • the vector Y comprises information 20 concerning the level of dilute pulp in the headbox, given by a sensor 20', information 21 concerning the concentration of dilute pulp in the headbox given by a sensor 21', information 22 concerning the total pressure in the headbox (or speed of jet), given by a sensor 22', and information 23 concerning the opening of the slice 17 given by a sensor 23'.
  • the vector Z comprises a set point 24 concerning the level in the headbox, a set point 25, concerning the concentration which is modified in accordance with the quality of the formation of the sheet (look-through) and the rapidity of drainage on the wire (position to the water line), a set point 26 concerning the speed of jet which is modified upon the optimization of the speed the machine and upon a grade change, and a set point 27 as to substance flow rate at the slice which is modified upon the control of the basis weight and upon a grade change.
  • the vector U comprises an order or signal 28 controlling the air valve actuator 14, an order 29 controlling the stock valve actuator 2, an order 30 controlling the pump actuator 3, and an order 31 controlling the slice opening actuator 17.
  • the vector P has been limited to a single component 32 which is information concerning the thick pulp consistency.
  • This information 32 which acts as a measurable disturbance can be introduced in all the following diagrams, in which it has not always been included, for reasons of simplification. It goes without saying that one can also use as the measurable disturbance any other component which is capable of being measured and capable of action on the outputs.
  • the measurement information given by a sensor may act, not as in conventional systems simply on a corresponding actuator or possibly two actuators, but on all the actuators the action of which is necessary, and do so in desired manner so that only the variable measured by said sensor is influenced.
  • FIG. 4 there is shown an example of a control system in accordance with the invention.
  • An action internal model 33 (for instance having the following inputs: stock valve, pump speed, air valve, slice opening) is put in parallel with the process 19 and it receives the same signals U(k) as the latter.
  • This action model 33 is defined by the following conventional relationships between the input U(k), the states X and the outputs Y:
  • A is a square output matrix of dimensions n.n
  • B and C are matrices whose dimensions depend on the number of inputs and outputs.
  • the matrices, A, B, C can be obtained directly by identification from input and output data of the process or from results of mathematical knowledge models such as, for instance, those in the article by P. A. A. Talvio entitled “A Study of Paper Machine Headbox Control System with Linear Transfer Functions", IFAC Congress London, 1966--Session 22--paper 22A and in the dissertation by A. Barraud: "Minimal Realization and Optimal Approximation of Invariant Linear Dynamic systems” (Dissertation for Degree of Doctor of Sciences--January 1978--ENSN Automation Laboratory GmbH).
  • An internal model of measured disturbances 34 is put in parallel with the process 19 and it receives the same measured disturbances Up(k) as the process 19 (for instance, i.e., thick-pulp consistency signal and possibly a measured variable used in a monovariable control).
  • This model also represented in discrete state variables, is of the same type as the model of action, and it can be obtained in the same manner.
  • the output signals Y(k) and Yp(k) respectively of the action model 33 and the disturbance model 34 are added in an adder 35 and the result of this addition is compared with the output signals Ys (k) of the process (for example, level, concentration of dilute pulp, speed of jet calculated on basis of the total pressure or measured directly, and rate of substance flow rate calculated on basis of the speed of the jet, the concentration and the slice opening) in a comparator 36 whose output constitutes the error signals E(k).
  • These signals E(k) are transmitted to a regulation reference model 37 whose output is transmitted to an adder 38.
  • This adder 38 also receives the output of a tracking reference model 39 receiving at its input the set points Z(k); the adder 38 also receives the output Yp(k) of the measured disturbances model 34.
  • the regulation reference model 37 and the tracking referece model 39 are selected in such manner that the system is decoupled. If a representation in state variables is selected, the matrices A, B and C are diagonal.
  • the output Yd (k) of the adder 38 is sent to an adder 40 (which gives U(k) at the output) via a matrix KYd 41 and an adder 42 receiving, in order to stabilize the system, the output U(k) of the adder 40 via a device 43 with delay ⁇ T and a matrix KUl 44.
  • the adder 40 receives the output X(k) of an adder 45 which receives the output of an action model 33 after being multiplied in a matrix KX 46.
  • the error signals E(k) are used to produce an anticipating action on the one hand by being transmitted by a matrix KE 47 to the adder 45 and on the other hand by entering into the action model 33 via a matrix KES 48.
  • the calculation of the matrices KX, KYd, KUl, KE, KES is based on the theory of optimal control by minimization of a quadratic criterion on a receding horizon.
  • FIG. 5 shows another embodiment of the control system in which one again finds most of the members of FIG. 4 except that some of them have been replaced by a calculation block 49 which receives on the one hand at 50 information concerning the constraints such as the limit variations of the actuators and outputs and the speed of variation of these actuators and outputs and, on the other hand, the outputs Yd(k) of the adder 38, U (k-1) of the delay device 43 and X(k) of the action model 33, and which supplies the control signals U(k).
  • this block realizes the functions represented in FIG. 4, that is to say the products of the matrices 41-44, 46-47 and the additions of the adders 40, 42, 45.
  • the optimization of the quadratic criterion is obtained by the use of non-linear programming methods such as the relaxation method, the modified gradient method, or the method of Frank and Wolf.
  • the system forming the object of the invention as just described makes it possible to take into account as a whole, for instance, four inputs and four outputs of the process and to decouple the outputs so as to be able to change the four outputs independently of each other and with the desired response.
  • This system can take into account disturbing variables which are measurable by means of sensors as well as constraints on the actions and on the outputs, in particular constraints of amplitude and speed of variation (for instance the speed of rotation of a slice-opening motor).
  • This system is easily integrated in the existing process controls such as the control of the basis weight and the moisture, the control of the ratio or the difference of jet speed/wire speed, and the optimizing of the production.
  • concentration at the headbox by means of an optical sensor makes it possible to calculate the substance flow rate from the measurement of the concentration, the slice opening and the total pressure, and thus to have a picture of what the basis weight will be at the end of the machine.
  • FIG. 6 a basis weight control diagram has been shown by way of example.
  • This diagram includes the system of FIG. 3 in which the substance flow rate set point 27 is supplied by a basis weight controller 51 which receives, at 52, measurement information from a basis weight sensor 53 located downstream of the drying section 54 and basis weight set point information 55.
  • the basis weight controller thus controls the substance flow rate set point but the control of the substance flow rate takes place locally with a rapid response due to the installation of an optical concentration sensor, which apparatus has up to now been considered as not to be used due to the fact that it can undergo measurement shifts while on the contrary it has been found that in the tests carried out in accordance with the invention these shifts were without importance since the control by the basis weight controller automatically provided for the necessary corrections.
  • FIG. 7 there is shown an example of control of the jet speed with respect to the wire speed.
  • a wire-speed sensor 56 whose measurement information 57 divides or subtracts the jet-speed information 58 deducted from the total pressure information 22 to give a value 59 of the ratio or difference of jet speed to wire speed which enters into a controller 60 receiving at 61 set point information ⁇ o and supplying at 62 set point 26 for jet speed (or total pressure in the headbox).
  • FIG. 6 and 7 the control of basis weight and the control of the ratio or difference of jet speed to wire speed, but it is obvious that these two controls can and will generally be run jointly.
  • the system in accordance with the invention has great stability and permits excellent decoupling of the different output variables of the process as well as a selection of the rapidity of response of these output variables.
  • Tests were carried out by changing the total pressure set point and there were observed the repercussions which this produced on the level and concentration in the headbox.
  • the result obtained with two monovariable control loops is shown in FIG. 8, in which there has been entered at 63, the variation of the total pressure, at 64 the variation of the level, and at 65 the variation of the concentration as a function of the time, the vector 66 indicating a period of one minute.
  • the result obtained with the multivariable system of the invention is shown in FIG.
  • the slice opening is not effected by a motor or else one cannot continuously control the slice opening (for reasons of mechanical endurance, for instance).
  • Three set points are introduced, namely level 24, speed jet 26, and substance flow rate 27.
  • the multivariable centralized control device 18 takes into account, at 70, a signal measuring the slice opening, as shown in FIG. 10, in order to eliminate its interaction on the level, jet-speed and substance flow outputs.
  • a diagram which, like that of FIG. 10, comprises a process with three inputs and three outputs can be used in the case of purely hydraulic headboxes, that is to say headboxes without air cushion, the air valve and the measurement of the level being eliminated.
  • the multivariable control system can take into account the variation of this output variable in measurable disturbance.
  • Two diagrams of such a system will be given by way of example for the situation where the level in the headbox is controlled independently of the multivariable centralized control device.
  • an analog control of the level in the headbox 7 has been installed by means of a level sensor 71 whose output 72 is compared in a controller 73 with set point 74 to control the air valve 14.
  • the output 72 of the sensor 71 is then sent as measurable disturbance 75 to the multivariable centralized control device 18.
  • FIG. 12 shows this last solution in which the control device 18 receives the information 20 as to level in the headbox, 21 as to concentration, 22 as to total pressure, and 23 as to slice opening and also as to level in the reverse 76.
  • a level set point 77 enters into the reverse.
  • the control orders comprise, in addition to the orders 28 to 31 concerning an air valve, stock valve, pump, and slice opening respectively, a control 78 which actuates the reverse rate-of-flow valve 79.
  • the level is maintained by overflow in a hole (so-called Hornbostel hole) the shape and dimensions of which are such as to obtain automatic control of the level.
  • Hornbostel hole the shape and dimensions of which are such as to obtain automatic control of the level.
  • a second solution comprises improving this first solution by taking into account the variation in level as a measurable disturbance in the multi-variable centralized control device.
  • a third solution comprises superimposing on the Hornbostel hole a level control incorporated in the multivariable constrol system as has been seen above and acting on the air valve to improve the precision on the level and eliminated the level/total-pressure interaction.
  • a second solution comprises permanently using these monovariable control loops, the multivariable centralized control device then acting not directly on the actuators of these loops but on the set points of the controllers of the monovariable control loops.
  • FIG. 14 shows such a solution.
  • a multivariable centralized control device 18 such as that of FIG. 3, for instance, in which the control order 28 no longer acts directly on the air valve 14 but on the set point of the controller 80 located in an analog control loop also comprising the level sensor and the air valve 14 and in which the control order 30 no longer acts directly on the pump 3 but on the set point of the controller 81 placed is an analog control loop also comprising the total pressure sensor and the pump 3.

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US06/223,564 1978-06-30 1981-01-08 Control system for papermaking machine headbox Expired - Fee Related US4374703A (en)

Applications Claiming Priority (2)

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FR7820428A FR2429867A1 (fr) 1978-06-30 1978-06-30 Commande du fonctionnement de la caisse de tete d'une machine a papier
FR7820428 1978-06-30

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US (1) US4374703A (enrdf_load_stackoverflow)
CA (1) CA1115573A (enrdf_load_stackoverflow)
DE (1) DE2926072A1 (enrdf_load_stackoverflow)
ES (1) ES482071A1 (enrdf_load_stackoverflow)
FR (1) FR2429867A1 (enrdf_load_stackoverflow)
GB (1) GB2025088B (enrdf_load_stackoverflow)
IT (1) IT1119789B (enrdf_load_stackoverflow)

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US20100174512A1 (en) * 2009-01-08 2010-07-08 Jonas Berggren Method and Apparatus for Creating a Generalized Response Model for a Sheet Forming Machine
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CN104746376B (zh) * 2015-04-17 2016-10-05 陕西科技大学 基于压缩空气鼓风的流浆箱进气量控制系统及其控制方法

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US20030089479A1 (en) * 1999-05-19 2003-05-15 Voith Sulzer Papiertechnik Patent Gmbh Device for controlling or regulating the basis weight of a paper or cardboard web
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US6733629B1 (en) * 1999-08-23 2004-05-11 Andritz Oy Method of controlling the operation of an approach system of a paper machine or the like web formation apparatus
US6421575B1 (en) * 1999-12-01 2002-07-16 Metso Paper Automation Oy Method and control arrangement for controlling sheet-making process
US20050016704A1 (en) * 2001-10-19 2005-01-27 Taisto Huhtelin Method and apparatus for controlling the operation of stock preparation of a paper machine
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US20090287319A1 (en) * 2008-03-26 2009-11-19 Attarwala Fakhruddin T Universal model predictive controller
US8126575B2 (en) * 2008-03-26 2012-02-28 Fakhruddin T Attarwala Universal model predictive controller
US20100174512A1 (en) * 2009-01-08 2010-07-08 Jonas Berggren Method and Apparatus for Creating a Generalized Response Model for a Sheet Forming Machine
US8155932B2 (en) 2009-01-08 2012-04-10 Jonas Berggren Method and apparatus for creating a generalized response model for a sheet forming machine
US20100179791A1 (en) * 2009-01-12 2010-07-15 Andreas Zehnpfund Method and Apparatus for Creating a Comprehensive Response Model for a Sheet Forming Machine
US8209048B2 (en) 2009-01-12 2012-06-26 Abb Automation Gmbh Method and apparatus for creating a comprehensive response model for a sheet forming machine
US20100198364A1 (en) * 2009-02-05 2010-08-05 Shih-Chin Chen Configurable Multivariable Control System
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DE2926072C2 (enrdf_load_stackoverflow) 1988-02-04
FR2429867B1 (enrdf_load_stackoverflow) 1982-04-02
GB2025088A (en) 1980-01-16
ES482071A1 (es) 1980-04-01
GB2025088B (en) 1982-12-15
FR2429867A1 (fr) 1980-01-25
IT7949586A0 (it) 1979-06-29
IT1119789B (it) 1986-03-10
DE2926072A1 (de) 1980-01-10

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